The present invention relates to petroleum processing, in particular to lubricant base oil and wax manufacture. The invention concerns the process of separation of petroleum wax from the occluded oil by virtue of precipitation of crystallized wax from the waxy feedstock and subsequent filtering and evacuation of the soft and hard wax from the mixture of dewaxed oil and solvent.
There are known numerous publications describing separating of petroleum wax from hydrocarbon oils in a waxy feedstock. The processes employed for this purpose are based on crystallization of wax from the feedstock, which is a mixture of slack wax, solvent and oil.
An example of such a process can be found in U.S. Pat. No. 5,196,116 in which there is disclosed a process for solvent dewaxing of a waxy oil feed to obtain petroleum oil lubricating stock. The process comprises the step of contacting of a warm waxy oil feed by indirect heat exchange first with cold filtrate and then with refrigerant to crystallize and precipitate the wax in the oil feed to form an oil/solvent/wax mixture. The disadvantage of this method is associated with the fact that it is not suitable to separation of petroleum oils having low pour point.
Typical method of crystallization can be found in a book xe2x80x9cLubricant base oil and wax processingxe2x80x9d p. 167-169, 1994 by Avelino Sequeira. According to this method the waxy feedstock is heated to 10-15 Degrees F above the cloud point of the oil/wax/solvent mixture and is diluted with a solvent while chilling at a controlled rate in double-pipe scraped surface exchanger and chiller. The shortcoming of this method is low filtration rate of the slurry and low yield of dewaxed oil and hard wax.
Unfortunately the known in the art methods of crystallization are not sufficiently efficient, since they can not ensure full separation of oils occluded within dendrite structure of crystallized wax.
There is known also an attempt to utilize ultrasonic energy for improving efficiency of the oil dewaxing process as described in an article xe2x80x9cUltrasound effect on oil dewaxing processxe2x80x9d by S. Abramovich et al., xe2x80x9cChemistry and Technology of Fuels and Oilsxe2x80x9d, No. 3, 1965, pp. 29-33. In accordance with this method ultrasonic energy of up to 2.5 kW was applied on laboratory scale to an oil-wax-solvent composition at 40 Degrees C and at cooling rate 120 Degrees C per hour. It has been revealed that ultrasonic treatment causes de-agglomeration of dendrites and thus may to a certain extent improve filtration rate and increase dewaxed oil yield. It has been observed however that ultrasonic treatment is effective only under 6-10 Degrees C below the cloud point. Further treatment under lower temperatures was ineffective because of the significant presence of solid phase in the mix and significant absorption of the ultrasonic energy. Due to the absorption one part of the crystals melts and the other part remains untreated at all. It can be assumed that the above phenomenon should be even more pronounced if the treatment is carried out on industrial scale, since it requires higher levels of ultrasonic energy.
Therefore despite numerous references disclosing technology of separation of hydrocarbon oils from petroleum wax there is nevertheless still felt a need in a new and improved method of separation.
The main object of the present invention is to provide for a new and improved method of separation and an apparatus for its implementation which will sufficiently reduce or overcome the above mentioned drawbacks of the known-in-the-art methods and apparatuses.
In particular the first other object of the invention is to provide for a new method of separation, which is based on crystallization of wax crystals and applying of ultrasonic energy to induce excretion of the occluded oils without however melting of the wax crystals.
Still further object of the invention is to provide for a new and improved method of separation and a system for its implementation in which the crystallization process is not deteriorated due to generation of heat associated with the applying of ultrasonic energy.
Yet another object of the present invention is to provide for a new and improved method of separation and a system for its implementation, which is not limited to the low pour point oils, which allows efficient separation with increased slurry filtration rate and which results in improved yield of dewaxed oil and hard wax.